Covering panel and process of producing covering panels

ABSTRACT

The present invention provides a covering panel, such as a floor panel, wall panel or ceiling panel, comprising a substrate and optionally a top layer, whereby said substrate comprises a synthetic material and a filler material, whereby said filler material is comprised in an amount from 15 to 75 wt. % based on the total weight of said substrate. In addition, the present invention provides a process of producing such covering panels.

This application is a division of Ser. No. 15/543,393 filed Jul. 13,2017, which claims the benefit of European Application No. 15151551.7filed Jan. 16, 2015, and PCT/EP2016/050733 filed Jan. 15, 2016,International Publication No. WO 2016/113377 A1, which are herebyincorporated by reference in their entirety as if fully set forthherein.

TECHNICAL FIELD

The present invention relates to the field of covering panels andprocesses of producing covering panels.

INTRODUCTION

Covering panels such as floor panels, wall panels and ceiling panels canbe obtained by laminating or calendaring multiple layers onto eachother, whereby each layer is provided with a specific functionality.Such panels are known in the state of the art.

I.e. WO 2013/026559 describes a floor panel in the form of a multilayer,rectangular laminate with a soft core of plastic, a decor film on theupper side of the core, a transparent finishing layer and a transparentlacquer layer applied on the finishing layer, as well as a back-pulllayer on the back of the core, with a lockable tongue and grooveconnection at least at two mutually opposite edges of the panel.

Other technologies provide panels with a distinctly differentcomposition. WO 2014/108465 discloses a specific composition comprisingat least propylene-based elastomer and polymer-containing waste of floorcovering, preferably polypropylene-containing carpet waste; and asurface covering in the form of a sheet, a panel, a tile or a plank, inparticular for covering a floor, wall, or ceiling in interior orexterior application, comprising the composition.

An important shortcoming of covering panels according to the state ofthe art, however, is a definite tendency to curling. Curling is oftenobserved in sheet-type articles which have a non-uniform compositionand/or contain zones of internal stress built up during processing. Morespecifically for laminate covering panels, it is believed that uponchanging temperatures of a multilayer laminate, different degrees ofshrinking and/or expansion of the separate layers constituting themultilayer laminate imparts either a positive or negative curling of thelaminate product. Due to curling, installed panels tend to becomenon-flat, decouple from each other, leading to issues of visual aspectsuch as for example gaps between panels. Furthermore, such panels sufferfrom impaired adhesion to the subsurface and can delaminate in case oflaminate panels. Other shortcomings relate to difficulties in cuttingthe panel material during installation to provide correct dimensions,and issues related to mechanical strength, sound and heat insulationand/or water resistant properties, and density or weight of the panel,which is of importance during transport and installation.

SUMMARY OF THE INVENTION

The current invention provides in a solution for at least one of theabove mentioned problems by providing a covering panel and process ofproducing covering panels, as described in the claims.

In a first aspect, the present invention provides a covering panel, suchas a floor panel, wall panel or ceiling panel, comprising at least onesubstrate and optionally a top layer, whereby said substrate comprises asynthetic material and a filler material, whereby said substratecomprises said filler material in an amount from 15 to 75 wt. % based onthe total weight of said substrate.

The substrate has a high rigidity which exhibits a reduced amount ofcurling of the finished covering panel. The feature of curling of thecovering panel is undesired since it limits the feasibility anddurability of the panel for use as a floor, wall or ceiling surfacecovering panel.

The inventors have surprisingly found that the degree of curling can besuppressed significantly by providing a covering panel with an optimisedamount of filler material according to the invention.

In a second aspect, the present invention provides a process ofproducing covering panels, such as floor panels, wall panels or ceilingpanels, each covering panel comprising at least one substrate andoptionally a top layer, whereby said at least one substrate comprises asynthetic material and a filler material; the method comprising thesteps of:

-   -   mixing said synthetic material and said filler material, thereby        obtaining a mixture;    -   extrusion of said mixture, thereby obtaining a substrate;    -   optionally, laminating said substrate to a top layer;

thereby obtaining a covering panel, whereby said filler material ismixed with said synthetic material in an amount from 15 to 75 wt. %based on the total weight of said mixture.

DETAILED DESCRIPTION OF THE INVENTION

The recitation of numerical ranges by endpoints includes all numbers andfractions subsumed within that range, as well as the recited endpoints.All percentages are to be understood as percentage by weight and areabbreviated as “wt. %”, unless otherwise defined or unless a differentmeaning is obvious to the person skilled in the art from its use and inthe context wherein it is used.

1. Covering Panel

The present invention relates to surface coverings, such as floorcoverings, constructed of rigid panels or tiles that can be assembledtogether for example by mechanical connections. Panels alone are oftenreferenced herein for the sake of simplifying the discussion. Wherever“panels” of the present invention are referenced herein, the descriptionthereof can be understood to apply equally to “tiles” unless indicatedotherwise.

The covering panel of the present invention can be any surface covering,such as a floor panel, wall panel, ceiling panel, and the like. Thecovering panel can be used essentially in any room in a house or workenvironment, including the kitchen, bathroom, living room, dining room,recreation room, garage, and outside living spaces, such as a porch,deck, shed, terrace, summerhouse, and the like. The covering panels ofthe present invention can be used in an indoor or outdoor applications,especially since the covering panels of the present invention are waterresistant and do not swell when wet. In fact, the swelling of thesurface coverings of the present invention is negligent (e.g., zero orzero to less than 0.01 mm or 0.0001 mm to less than 0.001 mm) whentested at LF 3.2 of NALFA LF 01-2003. Thus, the panel being waterresistant, can be used indoors or outdoors. For instance, the panels arewater resistant such that they will not swell when immersing in waterfor several hours. Further, the panels are resistant to variouschemicals and detergents and, therefore, can even be used in industrial,recreational, or garage environments.

When the substrate of the invention is provided in laminate form, thelaminate structure of the panel comprises different layers of plasticmaterials. It has excellent sound absorbing properties. The layers,especially the structure and composition of the substrate, contribute tothe sound absorbing function, so that the panel has an excellent qualityunder this aspect.

The definition of the phrase “laminate” as used in the present inventionshould be understood in the wider sense of the word, implying that alaminate constitutes two or more strata of materials. These materialsmay have different mechanical properties such as, but not limitedthereto; opacity, density, elastic modulus, elastic compression modulus,material composition, thermal conductivity, electrical conductivity,abrasion resistance, etc.

The covering panel can have any suitable length and/or width and can beprovided in any shape, such as a rounded shape and a polygonal shape(triangle, rectangle, square, pentagon, hexagon, heptagon or octagon).Preferably, the covering is provided in the shape of a square or arectangle. The panels of the present invention can also have a threedimensional shape, such as a corner-type shape which can usefully beemployed as a panel connection between surfaces which are perpendicularto each other for use in, for example, wall and ceiling coverings with aprinted design and an embossed surface, and even stairs. In onepreferred embodiment, the panel can be formed as a rectangle with twopairs of opposing sides wherein the pairs of sides can be the same ordifferent in length relative to each other. In one example, the panel isrectangular. The rectangular panel can have opposite shorter sideshaving a width, for example, of from 10 cm to 50 cm, preferably from 10cm to 30 cm or other widths, and opposite longer sides having a length,for example, of from 50 cm to 300 cm, preferably from 80 cm to 250 cm orother lengths. In one example, the panel also may be square shaped, andhave four sides of equal length. In some examples, surface coverings ofthe present invention can be, for example, square shaped panels. Thesizes of the present panels are not necessarily limited with respect tolarger sizes other than possibly by practical considerations such asrespect to handling, etc. The smaller sizes of the panels shouldadequately allow for the formation and use of the profiled edges on thepanel. In some examples, the panels have square shapes with a sidelength of from 20 cm to 100 cm, preferably from 25 cm to 80 cm, morepreferably from 30 cm to 60 cm, or other side lengths.

The covering panel according to the present invention may furthercomprise coupling parts for assembling several panels together. Couplingmechanisms have been widely used for many years and are well known tothe artisan. Most popular coupling parts are glueless locking systemswhere both horizontal and vertical locking of the panels are realisedwith a tongue along one (edge) side and a groove along the opposite(edge) side of the panel. Typically tongue and groove locking systemsare integrally made with the panel. An alternative locking systemcomprises a plurality of staggered hooking tongues, extending outwardlyfrom the edges of the panel. Such a system is for example described inEuropean patent application number 15151551.7, assigned to BerryAllocNV.

In a first aspect, the present invention provides a covering panel, suchas a floor panel, wall panel or ceiling panel, comprising at least onesubstrate and optionally a top layer, whereby said substrate comprises asynthetic material and a filler material, whereby said substratecomprises said filler material in an amount from 15 to 75 wt. % based onthe total weight of said substrate.

This is advantageous, because the optimised amount of filler materialprovides a substrate with high rigidity which exhibits a reduced amountof curling of the finished covering panel. The effect of curling of thecovering panel is undesired since it limits the feasibility anddurability of the panel for use as a floor, wall or ceiling surfacecovering panel. Ideally, such panels remain flat for long periods oftime under conditions of varying exposure to humidity, water andtemperature.

The substrate has a high rigidity, which imparts a reduced amount ofcurling of the finished covering panel. The feature of curling of thecovering panel is undesired since it limits the feasibility anddurability of the panel for use as a floor, wall or ceiling panel.

Without limiting to any theoretic or mechanistic implications, it isbelieved that due to non-uniform technical characteristics of a layer,and in case of laminate upon exposure to temperature differences,different degrees of shrinking and/or expansion of the separate layersconstituting the multilayer laminate, impart either a positive ornegative curling of the product, such as a covering panel.

Faced with the problem of curling of a covering panel, the personskilled in the art would be tempted to introduce a reinforcing layer,i.e. a glass fibre nonwoven, in order to enhance rigidity of thecovering panel, thereby reducing any curling effects. The inventors havesurprisingly found that the degree of curling can be suppressedsignificantly by providing a covering panel with an optimised amount offiller material according to the invention.

Another important advantage of the present panel is that it can be cutwith a sharp strong knife. No saw is necessary to cut the panel intopieces, because it only comprises layers of plastic materials. Thismakes the installation process very easy even for inexperienced persons.In most cases even cutting at the surface of the panel is sufficient tocreate a weakening line at the upper surface of the panel so that it canbe broken along this line afterwards.

In a preferred embodiment, the substrate is comprised with a thicknessof 1 mm to 5 mm. In one embodiment, the substrate is comprised with athickness of 1.0 mm to 2.5 mm, and more preferably with a thickness of1.5 mm to 2.0 mm. Such covering panels can be usefully employed, i.e.for wall covering or ceiling panels where requirements for very highmechanical strength is limited. In one embodiment, the substrate iscomprised with a thickness of 2.5 mm to 4.5 mm, and more preferably witha thickness of 3.0 mm to 4.0 mm. Such covering panels can be usefullyemployed, i.e. for floor panels where requirements for mechanicalstrength are high, but where the specific surface weight (gsm) of thepanel is preferably low in order to allow for an environmentallyfriendly transport and ease during installation.

1.1 Synthetic Material

The term “synthetic material” as used in the context of the currentinvention, is to be understood as comprising one polymer or a blend oftwo or more polymers. The synthetic material can be comprised of any oneor more polymers. For instance, the synthetic material can be comprisedof a thermoplastic or thermoset polymer. The synthetic material can becomprised of any polymer, including mixtures of natural and syntheticpolymers. The synthetic material can be, for example, a thermoplasticpolymer, a thermosetting polymer, a rubber (elastomer), or anycombinations thereof. Further, the synthetic material can be comprisedof, for example, any type of polymer, such as a homopolymer, acopolymer, a random polymer, alternating polymer, graft polymer, blockpolymer, star-like polymer, comblike polymer, crosslinked polymer,and/or vulcanized polymer. The synthetic material can be comprised ofone or more polyblends. The synthetic material can be, for example,comprised of a thermoplastic elastomer (TPE), an interpenetratingpolymer network (IPN); simultaneous interpenetrating polymer network(SIN); or interpenetrating elastomeric network (IEN).

In a preferred embodiment, the present invention provides a coveringpanel according to the first aspect of the invention, whereby saidsynthetic material is a thermoplastic material or thermosetting materialor mixtures thereof.

The synthetic material can be, for example, comprised of asilicone-containing polymer, for instance, polydimethyl siloxane,fluorosilicones, silicone-organic polymers, or silicone-organic hybridpolymers. Other examples of synthetic materials include, but are notlimited to, olefin-containing, diene-containing and butene-containingpolymers and copolymers. Examples of elastomers comprise solutionstyrene-butadiene rubber (SBR), natural rubber, emulsion SBR,polybutadiene, polyisobutadiene, polyisoprene, polychloroprene, NBR,EPDM, EPM, isobutene elastomers, and their functionalized or modifiedderivatives or blends thereof. Other examples of polymers include, butare not limited to, linear and nonlinear polymers such as polyethylene,poly(vinylchloride), polyisobutylene, polystyrene(s), polycaprolactam(nylon), polyisoprene, and the like. Other general classes of polymersinclude polyamides, polycarbonates, polyelectrolytes, polyesters,polyethers, (polyhydroxy)benzenes, polyimides, polymers containingsulfur (such as polysulfides, (polyphenylene) sulfide, andpolysulfones), polyolefins, polymethylbenzenes, polystyrene and styrenecopolymers (ABS included), acetal polymers, acrylic polymers,acrylonitrile polymers and copolymers, polyolefins containing halogen(such as polyvinyl chloride and polyvinylidene chloride), celluloseacetate, ethylene-vinyl acetate, polyacrylonitrile, fluoropolymers andfluoroplastics, ionomeric polymers, polymers containing ketone group(s),polyketone, liquid crystal polymers, polyamide-imides,polyaryletherketone, polymers containing olefinic double bond(s) (suchas polybutadiene, polydicyclopentadiene), polyphenylene oxides,polyurethanes, thermoplastic elastomers, polyolefins (such aspolyethylene, 1-butene, polypropylene, 1-hexene, 1-octene,4-methyl-1-pentene, substituted alpha-olefins, and the like), polyolefincopolymers (such as copolymers of: ethylene, 1-butene, propylene,1-hexene, 1-octene, 4-methyl-1-pentene and substituted alpha-olefins andthe like), polyolefin terpolymers, polycarbonates, silicone polymers,alkyd, epoxy, unsaturated polyester, vinyl ester, urea-, melamine-, orphenol-formaldehyde resins, and the like. Other examples of the polymercan be an acrylic polymer, a methacrylic polymer, or a styrenic polymeror silicone polymer. The polymer present in the synthetic material ofthe present invention can be a polyolefin. The molecular weight of thepolymer can be, for example, from 10,000 to 1,000,000, or from 50,000 to500,000, or from 100,000 to 200,000, or other values, based on weightaverage molecular weight.

In one particular example, the polymeric material is a thermoplasticpolymer that includes, but is not limited to, vinyl containingthermoplastics such as polyvinyl chloride, polyvinyl acetate, polyvinylalcohol, and other vinyl and vinylidene resins and copolymers thereof;polyethylenes such as low density polyethylenes and high densitypolyethylenes and copolymers thereof; styrenes such as ABS, SAN, andpolystyrenes and copolymers thereof, polypropylene and copolymersthereof; saturated and unsaturated polyesters; acrylics; polyamides suchas nylon containing types; engineering plastics such as polycarbonate,polyimide, polysulfone, and polyphenylene oxide and sulfide resins andthe like.

In a preferred embodiment, said thermoplastic material is comprised of apolymer or a blend of two or more polymers with a high degree ofamorphous phase and a low degree of crystallinity as determined byDifferential Scanning calorimetry in a nitrogen atmosphere from roomtemperature to 250° C. with the temperature increasing by 10° C./min.,measured according to ISO 11357-2. In a preferred embodiment, saidpolymer or a blend of two or more polymers is comprised with a degree ofcrystallinity of less than 40% as measured by Differential Scanningcalorimetry. More preferably, said degree of crystallinity is less than20% and even more preferably less than 10%. Most preferably, said degreeof crystallinity is 0%, 2%, 4%, 6%, 8%, 10%, or any value there inbetween. This is advantageous because a thermoplastic materialcomprising a polymer or a blend of two or more polymers with a highdegree of amorphous phase shows a reduced degree of shrinking duringcooling of the thermoplastic melt and exhibits an enhanced dimensionalstability. Furthermore, such polymers or blend of polymers show goodimpact resistance as well as excellent processability during secondaryprocessing, such as bending fabrication and high-frequency bonding.

The synthetic material to be processed can be in powder, liquid, cubed,pelletized form or any other extrudable form. Also, the syntheticmaterial can be virgin, recycled, or a mixture of both. Furthermore, thesynthetic material can be incorporated with a blowing agent(s) or amechanically injected gas or a supercritical fluid such as supercriticalcarbon dioxide during the extrusion process to make a cellular foamstructure.

The synthetic material used to form the substrate, which can bepolyvinyl chloride, can be a suspension grade or mass polymerizationgrade homopolymer resin having a preferred molecular weight as reflectedby their K-value. The K-value of a polymer is a measure for the polymerchain length and is described in detail by K. Fikentscher in“Cellulosechemie”, 13, 58 (1932). A preferred K-value of a polymer in asynthetic material is comprised between 60 and 70, and preferably themolecular weight distribution and particle size distribution are narrowin order to provide a good balance between processability and materialproperties. Also, high porosity and uniform porosity of the resinparticles are preferred to optimize compounding and processing aspects,including the fast and uniform absorption of any stabilizer that ispresent as well as other ingredients during compounding. A syntheticmaterial compound used to form the substrate can be a PVC powdercompound that has good impact strength, ease of processing, highextrusion rate, good surface properties, excellent dimensionalstability, and indentation resistance.

In one example, the synthetic material can comprise a vinyl chloridehomopolymer and a vinyl copolymer, such as a vinyl chloride-vinylacetate copolymer, wherein the vinyl chloride homopolymer can be presentin the composition in an amount from about 1 wt. % to greater than 50wt. % of the combined amount of vinyl chloride homopolymer and a vinylcopolymer, such as vinyl chloride-vinyl acetate copolymer (e.g., fromabout 1 wt. % to about 20 wt. %, from about 20 wt. % to about 40 wt. %,from about 40 wt. % to about 60 wt. %, from about 60 wt. % or greater,about 65 wt. % or greater, about 70 wt. % or greater; or from about 75wt. % to about 99 wt. %). As a non-limiting example, the amount of vinylchloride homopolymer in the virgin polymer can be from about 80 wt. % toabout 99 wt. % of the combined amount of vinyl chloride homopolymer andvinyl chloride-vinyl acetate copolymer, or may be from about 70 wt. % to99 wt. % (or more) of the combined amount of vinyl chloride homopolymerand vinyl chloride-vinyl acetate copolymer or may be from about 80 wt. %to 90 wt. % of the combined amount of vinyl chloride homopolymer andvinyl chloride-vinyl acetate copolymer. The vinyl chloride copolymer andhomopolymer can have any K-value or molecular weight, and preferablyhave a K-value between 50 and 70, more preferably between 55 and 65 andmost preferably of 56, 58, 60, 62 or 64, or any value there in between.

1.2 Filler Material

The substrate further comprises at least one filler or filler sourcesuch as post-industrial recycled or post-consumer recycled materialssuch as gypsum, glass, energy by-products, wood, plastic, or partsthereof, PVC, VCT recycled, and the like, or all of these.

The filler can further include any other filler, including anyconventional filler, which can be used in solid vinyl tiles, and/orrubber compositions. The filler can be natural filler or syntheticfiller. The filler can be in the form of particles, short fibres,flakes, and other discrete forms. In a panel having a substrate,inorganic filler is preferably used. Examples of inorganic filler caninclude, but are not limited to, hydrated alumina, magnesium carbonate,calcium sulfate, silica, precipitated silica, fumed silica, fly ash,cement dust, glass, clay, chalk, limestone, marble, talc, calciumcarbonate, barium sulfate, silicates, aluminium trihydrate, kaolin,wollastonite, gypsum, solid or hollow glass microspheres, and the like.Inorganic fillers can be, for example, mineral fillers. The filler alsocan be non-mineral or organic filler such as carbon black, wood flour,cellulose-derived materials, ground rice hulls, solid or hollowtemperature resistant polymer microspheres or microbeads (e.g., phenolicmicrospheres), and the like. Carbon black, for example, can be used asfiller in rubber-based substrate, or other types of substrate panels.The inorganic and organic fillers can be used in combinations in thesubstrate, or either type can comprise the sole type of filler used inthe substrate.

In a preferred embodiment, the synthetic material further comprisesnatural fibres, preferably natural fibres derived from plant origin,such as fruit fibres, such as coconut (coir) fibres; seed fibres, suchas cotton fibres, kapok fibres; bast fibres, such as flax fibres, hempfibres, jute fibres, ramie fibres, rattan fibres, vine fibres; leaffibres, such as sisal fibres, banana fibres, agave fibres, abacá fibres;and stalk fibres, such as wheat fibres, rice fibres, barley fibres, treewood fibres, grass fibres, bamboo fibres. In a preferred embodiment,said natural fibres comprise cellulose fibres such as cotton and flax,hemicellulose fibres and/or processed cellulose fibres such as rayon,viscose and cellulose-acetate fibres. In many cases, these fibres canprovide an alternative to generally used reinforcement layers such as,i.e. glass fibre layers, and thus offer an environmentally benignalternative to glass fibres. In addition, carefully selected naturalfibres such as tree wood fibres allow to provide for a natural look, andwhen comprised in high amounts in said synthetic material as topartially penetrate the surface, even a natural feel of the accordinglyobtained substrate. In a preferred embodiment, said natural fibres arecomprised in an amount of 1 wt. % to 20 wt. %, based on the total weightof said substrate. More preferably, said natural fibres are comprised inan amount of 2 wt. % to 5 wt. %.

As indicated, an inorganic filler is preferably used in a substrate. Aninorganic filler typically provides dimensional stability and reducedelasticity to a vinyl tile, and may provide properties of fireresistance. As a non-limiting example, limestone (e.g., calciumcarbonate with magnesium carbonate) may be used as the filler. As apreferred, non-limiting example, an inorganic filler can be used for thefull amount of filler described for a substrate formulation herein, orother proportions (e.g., at least about 50 wt. %, or at least about 60wt. %, or at least about 70 wt. %, or at least about 80 wt. %, or atleast about 90 wt. %, or at least about 99 wt. %, up to 100 wt. % of allfiller). As another non-limiting example, a mineral filler, such as aparticulate mineral filler, can be used for the full amount of inorganicfiller described for a substrate formulation herein, or otherproportions (e.g., at least about 50 wt. %, or at least about 60 wt. %,or at least about 70 wt. %, or at least about 80 wt. %, or at leastabout 90 wt. %, or at least about 99 wt. %, up to 100 wt. % of allinorganic filler). In other examples, such as for some rubber-basedsubstrate, an organic or non-mineral filler such as carbon black can beused for the full amount of filler described for a substrate formulationherein, or other proportions (e.g., at least about 50 wt. %, or at leastabout 60 wt. %, or at least about 70 wt. %, or at least about 80 wt. %,or at least about 90 wt. %, or at least about 99 wt. %, up to 100 wt. %of all filler).

In a first preferred embodiment, the present invention provides acovering panel according to the first aspect of the invention, whereinsaid filler material is present in an amount from 20 to 60 wt. % basedon the total weight of said substrate.

In a second preferred embodiment, the present invention provides acovering panel according to the first aspect of the invention, whereinsaid filler material is present in an amount from 40 to 70 wt. % basedon the total weight of said substrate.

In a third preferred embodiment, the present invention provides acovering panel according to the first aspect of the invention, whereinsaid filler material is present in an amount from 10 to 50 wt. % basedon the total weight of said substrate.

In a preferred embodiment, said substrate comprises a filler material,said filler material being comprised predominantly of a mixture of chalkand talc. Thereby, it is meant that at least 50 wt. % and morepreferably at least 80 wt. % of said filler material is comprised ofchalk and talc. Most preferably, said filler material is comprised of atleast 95 wt. % of chalk and talc.

In a preferred embodiment, the present invention provides a coveringpanel according to the first aspect of the invention, wherein saidfiller material is comprised of a mixture of chalk and talc in a ratioof 50:1 to 1:50, based on wt. %.

In a more preferred embodiment, said filler material comprises a mixtureof chalk and talc in a ratio of 20:1 to 1:2, based on wt. %, morepreferably in a ratio of 8:1 to 1:1, based on wt. %. Most preferably,said ratio is 8:1, 7:1, 6:1, 5:1, 4:1, 3:1 or 2:1, or any ratio there inbetween. Especially preferred is a chalk to talc ratio of 2:1. This isadvantageous, because accordingly a substrate with high elasticitymodulus is obtained. This allows to optimise the weight/stability ratioof the panel, e.g. by optimising the void volume of the panel, as isexplained hereinafter. In one preferred embodiment, the substrate isrigid. The term “rigid” in the context of the present invention refersto a characteristic of a substrate or panel with an E-modulus of 1200MPa or higher, measured according to ISO 527, a glass transitiontemperature (T_(g)) of 60° C. or higher, measured according to ISO11357-2 and a Vicat temperature of 50° C. or higher, measured accordingto ISO 306-A-50. Preferably, said substrate has an E-modulus of 2000 MPaor higher and more preferable an E-modulus of 4000 MPa or higher. Usingan optimised amount of talc and chalk, a substrate with an E-modulus upto 8000 MPa can reasonably be achieved. Preferably, said substrate has aglass transition temperature (T_(g)) of 75° C. or higher and morepreferable a glass transition temperature (T_(g)) of 85° C. or higher.Preferably, said substrate has a Vicat temperature of 70° C. or higherand more preferable a Vicat temperature of 80° C. or higher.

In a preferred embodiment, the present invention provides a coveringpanel according to the first aspect of the invention, whereby said chalkis comprised of particles with at least 95% of said particles having aparticle size less than 25.0 μm, measured according to ISO 13317-3. In amore preferred embodiment, the present invention provides a coveringpanel according to the first aspect of the invention, whereby said chalkis comprised of particles with at least 95% of said particles having aparticle size less than 10.0 μm, measured according to ISO 13317-3.

The inventors have surprisingly found that said dimensions of particlesize of said chalk, when incorporated in a polymeric matrix, even ifmerely in only one or several plastic layers, assist in improving therigidity of substrate.

In a preferred embodiment, the present invention provides a coveringpanel according to the first aspect of the invention, whereby said talcis comprised of particles with at least 95% of said particles having aparticle size less than 100.0 μm, measured according to ISO 13317-3. Ina more preferred embodiment, the present invention provides a coveringpanel according to the first aspect of the invention, whereby said talcis comprised of particles with at least 95% of said particles having aparticle size less than 25.0 μm, measured according to ISO 13317-3.

This is advantageous, because said dimensions of particle size of saidtalc, when incorporated in a polymeric matrix such as a plastic layer,assist in improving the rigidity of said substrate.

The substrate can be comprised, for example, of one or more substratelayers comprising a blend of polymer material and filler in sheet form.The synthetic material can form, for example, a continuous phase intowhich the filler is dispersed as a discrete phase. In another example,the substrate can comprise a laminate of diverse layers including one ormore substrate layers (e.g., two or three or more substrate layers thatcan be the same or different with respect to composition and/or physicalproperties), each layer comprising a blend of synthetic material andfiller.

In one embodiment, the substrate comprising a synthetic material and aminor amount of inorganic filler can have a print design or film appliedover a substrate(s) or other intermediate layers with a clear (e.g.,vinyl) wear layer(s) on top of the print film.

In various options, the substrate of the panel of the present inventioncan comprise one or more rubber or elastomer materials and at least onefiller material. The rubber or elastomer can be present in the sameamounts as those given for the thermoplastic polymer material, such asPVC, described herein. The rubber or elastomer can be the predominantcomponent (by weight) in the substrate. As an option, the rubber orelastomer can be a substitute for the thermoplastic or PVC ingredientthat can be used in the substrate. The rubber or elastomer component canbe considered a polymer for purposes of the present invention. Therubber-based substrate of the present panels can be comprised of rubber(elastomer), fillers, and optionally pigment. The rubber can be, forexample, a vulcanizable rubber, a reaction system elastomer, athermoplastic elastomer, or other elastomers. Some filler, such ascarbon black or others, also may function like a pigment to impartcolour to the substrate. The amount of filler in the rubber-basedsubstrate is specifically limited, and can range, for example, fromabout 15 wt. % to about 75 wt. %, or from about 30 wt. % to about 70 wt.%, or other amounts, based on the total weight of the substrate.

1.3 Top Layer

In one embodiment, said laminate structure is comprised of saidsubstrate and a top layer. In one embodiment, a top layer comprises aprint layer and a wear layer. The top layer is integrally attached to anupper surface of the substrate. The top layer also optionally can havean underlay below the printed design and a protective layer on top ofthe wear layer. The top layer(s) can be, for example, PVC, olefins,urethane, ionomer, acrylic, polyester, thermoplastic polyolefin (TPO),thermoset polyurethane (TPU), or other materials conventionally used forthis type of layer(s) or materials. The protective layer can be, forexample, a thermally cured system such as water based polyurethanedispersion system, water based acrylic, or vinyl emulsion coating, or aradiation cured coating system such as urethane epoxy or polyesteracrylates, or other materials conventionally used for this type of layeror materials.

In one embodiment, the top layer further comprises natural fibres.Preferably, said natural fibres are derived from plant origin, such asdescribed above. Carefully selected natural fibres can be selected fromthe list of natural fibres such as described above. For example, treewood fibres allow to provide for a natural look, and when comprised inhigh amounts in said synthetic material. In a preferred embodiment, saidnatural fibres are comprised in an amount of 1 wt. % to 20 wt. %, basedon the total weight of said top layer. More preferably, said naturalfibres are comprised in an amount of 2 wt. % to 5 wt. %.

As indicated, some present panels can have a laminate construction, suchas a laminate structure of a rigid substrate comprised of syntheticmaterial and an amount of inorganic filler. In the laminate, thesubstrate contains a multilayer substrate, which in this embodiment canbe referenced as a laminate substrate, and this substrate has a topsurface, and located or affixed on the top surface of the substrate is aprint layer. The print layer has a top surface and a bottom surface.Affixed onto the top surface of the print layer is a wear layer having atop surface and a bottom surface. An underlay layer optionally can belocated and affixed between the bottom surface of the print layer andthe top surface of the substrate. The present panels do not require abacking layer, but can optionally have a backing layer. Said backinglayer can comprise a synthetic material and natural fibres, preferablyin an amount of 1 wt. % to 20 wt. %, based on the total weight of saidbacking layer, and more preferably, in an amount of 2 wt. % to 5 wt. %.

1.4 Printed Design

In one embodiment, the print layer can be, for example, printed PVCfilm. The print layer can be, for example, a printed design, such as tosimulate various wood grains. Generally, the print layer can be preparedby rotogravure printing techniques or other printing means such asdigital printing.

In one embodiment, the substrate is produced by extrusion of at leastone thermoplastic material comprising a filler material in an amount of15 to 75 wt. % based on the total weight of said substrate, optionallycomprising one or more colorants, wood-fibres, wood-particles, etc.,after which a print pattern is directly applied on the substrate. Theprint pattern may be directly applied on the substrate using anytechnique known in the art. Preferably, the print pattern is applied tothe substrate by laser printing, inkjet printing, intaglio printing,screen printing or any combination of the previous. Preferably, theprint pattern is applied using a digital printing technique, such asinkjet printing or laser printing. The use of digital printingtechniques improves the applicability of the process and allows a higherdegree flexibility of the print patterns that can be applied on thesubstrate as compared to analogue printing techniques such as screenprinting and intaglio printing. Other preferred embodiments comprising aprint pattern directly applied onto the substrate are described in aco-pending European patent application Nº EP15151552.5, entitled‘Covering and method for producing covering panels’ filed by theApplicant on 16 Jan. 2015.

1.5 Wear Layer

The wear layer can be made of any suitable material known in the art forproducing such wear layers, such as a polymeric film or overlay paper.The wear layer can be, for example, a transparent polyvinyl chloridelayer. The dry film thickness of this PVC wear layer is preferably fromabout 0.10 mm to about 1.00 mm, and more preferably from about 0.25 mmto about 0.70 mm. Other examples of this wear layer include, but are notlimited to, acrylic polymers, polyolefins, and the like. The wear layercan be a plasticized or a rigid polyvinyl chloride composition and/orother polymers, such as clear polymers. Optionally, the wear layerfurther comprises a topcoat which can be a thermoset layer or athermoplastic layer. The wear layer top coat can be, for example, awater based, solvent based, radiation-curable, non-radiation curable,UV-curable or non-UV-curable system. For example, the wear layer topcoat can be comprised of acrylics, acrylates, urethanes, epoxies, othertypes vinyl, other type polymers, and blends thereof, as long as thecomposition when cured, results in a rigid, thermoset coating withadequate cross-link density.

In the present invention, one or more layers can contain wear resistantparticles, such as a wear layer and/or wear top coat layer (e.g.,protective layer). One example is at least one layer containingaluminium oxide. The aluminium oxide used in the present invention isalso known as alumina or Al₂O₃. The aluminium oxide can be fused orcalcined. The refractive index can be from about 1.4 to about 1.7.

A sufficient amount of the aluminium oxide and/or other wear resistantparticles can be present in at least one layer of the surface coveringto provide improved wear and/or stain resistance to a surface coveringas compared to no aluminium oxide being present. From about 2 gsm toabout 50 gsm, or from about 4 gsm to about 20 gsm of alumina, forexample, can be present in at least one layer of the surface covering.Alternatively, from about 1 wt. % to about 40 wt. % of alumina can bepresent in at least one layer of the surface covering. Also, while anysource of aluminium oxide can be used, the aluminium oxide can have thefollowing characteristics: fused or calcined and having a hardness offrom about 6 to about 9 on a Mohs scale, and most preferably about 9 ona Mohs scale. The particle size of the aluminium oxide can be, forexample, from about 10 microns to about to about 70 microns, or fromabout 20 microns to about 50 microns. Sources of aluminium oxide areWashington Mills, N. Grafton, Mass.; ALCOA Industrial Chemicals,Bauxite, Ark.; Composition Materials, Fairfield, Conn.; Micro Abrasives,Westfield, Mass.; and Alu Chem, Inc., Birmingham, Ala. The aluminiumoxide, which can be part of at least one layer of the surface covering,can be added in any manner known to those skilled in the art for addingparticles to a layer. The aluminium oxide can be mixed into a wetcoating or scattered on top of a wet coating. The aluminium oxide canbe, for example, applied by a pellet dispenser, which applies orsprinkles aluminium oxide on top of a layer which is still “wet” oruncured. By the layer being “wet” or uncured, the aluminium oxide“sticks” or adheres to the “wet” layer and at least a portion of thealuminium oxide “sinks” into the layer and thus is not exposed to theenvironment. Instead of alumina, other metal oxides or ceramics can beused.

1.6 Void Volume

In a preferred embodiment, the present invention provides a coveringpanel according to the first aspect of the invention, wherein saidsubstrate has a void volume from 10 vol. % to 70 vol. %. The provisionof a rigid covering panel with optimised filler content and a high voidvolume allows for a low weight of the covering panel without negativelyimpacting the mechanical durability of the panel. This is advantageous,because low weight of said panels is beneficial during transport andinstallation, while the excellent mechanical properties providedurability to the panels.

In one embodiment, the covering panel can comprise a substrate with avoid volume from 10 vol. % to 70 vol. %, whereby said substratecomprises a foam of an open-cell structure. Open-cell means that the gasin that cell is not so restricted and is able to flow without passingthrough any polymer cell walls to the atmosphere. When filled with i.e.air or any similar gas, said substrate provides a relatively goodinsulator. In a preferred embodiment, said substrate is comprised with avoid volume from 20 vol. % to 60 vol. %, more preferably from 35 vol. %to 50 vol. %.

In one embodiment, the covering panel can comprise a substrate with avoid volume from 10 vol. % to 70 vol. %, whereby said substratecomprises a foam of a closed-cell structure. Closed-cell means that thegas within that cell is isolated from another cell by the polymer wallsforming the cell. Accordingly, a substrate with comparatively highercompressive strength is obtained. Preferably, the closed-cells arefilled with a specialized gas to provide improved insulation. Coveringpanels comprising one or more closed-cell structure foams exhibit higherdimensional stability, low moisture absorption coefficients, and higherstrength. In a preferred embodiment, said substrate is comprised with avoid volume from 30 vol. % to 70 vol. %, more preferably from 45 vol. %to 60 vol. %.

In one embodiment, the covering panel can comprise a multilayersubstrate with a void volume from 10 vol. % to 70 vol. %, whereby saidsubstrate comprises at least a first layer comprising a foam of aclosed-cell structure. Each foam layer comprises a foam syntheticcomposition. A foam synthetic composition comprises a continuouspolymeric matrix material and filler material with cells definedtherein. Cellular (foam) has the meaning commonly understood in the artin which a polymer has a substantially void volume comprised of cellsthat are closed or open. Said multilayer substrate can further comprise3, 4, 5, 6, 7, 8, 9 or 10 foamed layers, or a combination of foamed andnon-foamed layers.

In one embodiment, the covering panel can comprise a substrate with avoid volume from 10 vol. % to 70 vol. %, whereby said substratecomprises a foam with a mixed closed-cell structure and open-cellstructure. The volume percentage of open and closed cells, is determinedaccording to ISO 4590. A closed-cell foam has less than 30 percent,preferably 20 percent or less, more preferably 10 percent or less andstill more preferably 5 percent or less and most preferably one percentor less open-cell content. A closed-cell foam can have zero percentopen-cell content. Conversely, an open-cell foam has 30 percent or more,preferably 50 percent or more, still more preferably 70 percent or more,yet more preferably 90 percent or more open-cell content. An open-cellfoam can have 95 percent or more and even 100 percent open-cell content.

Desirably, the foams of the foamed substrate comprise synthetic foam,which is a foam composition with a polymeric continuous matrix materialand filler material. Any polymeric foam is suitable including extrudedpolymeric foam, expanded polymeric foam, free rise or restrained riseliquid dispensed polymeric foam, and moulded polymeric foam. The foamsmay comprise, and desirably comprises as a continuous phase,independently a thermoplastic polymer matrix material and/or a thermosetpolymer matrix material. In other words, one foam layer may be athermoplastic polymeric foam and the other foam layer may be a thermosetpolymeric foam, both foam layers may be thermoset polymeric foams, orboth foam layers may be thermoplastic polymeric foams. Desirably, boththe first and second foam polymeric matrix material have a thermoplasticpolymeric continuous phase comprising filler material.

1.7 Foaming Agent

The term “foaming agent” or “blowing agent”, used herein as synonyms,refers to a compound capable of forming a cellular structure in a widevariety of materials, typically under the influence of heat, via afoaming process. Such cellular structure typically lowers the density ofthe material and typically results in an expansion in volume of thematerial. The blowing agent in the foamed plastic-based material mayinclude at least one selected from a chemical blowing agent, a physicalblowing agent, or a mixture thereof. Physical blowing agents aretypically added to the material in a liquid phase, after which thetemperature is raised, thereby transforming the blowing agent into itsgaseous phase, and hence resulting in the formation of a cellularstructure and the expansion of the material, though they may also bedirectly added to the material in their gaseous phase. Chemical blowingagents will undergo a chemical reaction under the influence of heat,thereby forming gaseous products that will form the cellular structure.As the chemical blowing agent, any compound may be used as long as thecompound may be decomposed at a specific temperature to generate gas,and an example thereof may include azodicarbonamide,azodi-isobutyro-nitrile, benzenesulfonhydrazide, 4,4-oxybenzenesulfonyl-semicarbazide, p-toluene sulfonyl semicarbazide, bariumazodicarboxylate, N,N′-dimethyl-N,N′-dinitrosoterephthalamide,trihydrazino triazine, sodium bicarbonate, potassium bicarbonate,ammonium bicarbonate, sodium carbonate, ammonium carbonate, as well asany derivative of the previous or any combination of the previous.Further, examples of a physical blowing agent may include an inorganicblowing agent such as carbon dioxide, nitrogen, oxygen, argon, water,air, helium, or the like, or an organic blowing agent such as aliphatichydrocarbons containing 1 to 9 carbon atoms, including methane, ethane,propane, n-butane, isobutane, n-pentane, isopentane, neopentane,cyclobutane, and cyclopentane; fully and partially halogenated alkanesand alkenes having from one to five carbons, preferably that arechlorine-free (e.g., difluoromethane (HFC-32), perfluoromethane, ethylfluoride (HFC-161), 1,1-difluoroethane (HFC-152a), 1,1,1-trifluoroethane(HFC-143a), 1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1,2tetrafluoroethane (HFC-134a), pentafluoroethane (HFC-125),perfluoroethane, 2,2-difluoropropane (HFC-272fb), 1,1,1-trifluoropropane(HFC-263fb), 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea),1,1,1,3,3-pentafluoropropane (HFC-245fa), and1,1,1,3,3-pentafluorobutane (HFC-365mfc)); fully and partiallyhalogenated polymers and copolymers, desirably fluorinated polymers andcopolymers, even more preferably chlorine-free fluorinated polymers andcopolymers; aliphatic alcohols having from one to five carbons such asmethanol, ethanol, n-propanol, and isopropanol; carbonyl containingcompounds such as acetone, 2-butanone, and acetaldehyde; ethercontaining compounds such as dimethyl ether, diethyl ether, methyl ethylether and carboxylate compounds such as methyl formate, methyl acetate,ethyl acetate and carboxylic acid, or any combination of the previous.

The amount of blowing agent can be determined by one of ordinary skillin the art without undue experimentation for a given synthetic materialto be foamed based on the type of synthetic material, the type ofblowing agent, and the desired foam density. The foam density,typically, is selected depending on the particular application.Preferably, the foam density is equal to or less than about 1600 kg/m³,more preferably less than about 1400 kg/m³, even more preferably lessthan about 1300 kg/m³, and most preferably less than about 1200 kg/m³. Afoam density of less than about 1150 kg/m³ is especially preferred.Preferably the foam density is equal to or more than about 400 kg/m³,more preferably more than about 600 kg/m³, even more preferably morethan about 800 kg/m³, and most preferably more than about 1000 kg/m³. Afoam density of more than about 1050 kg/m³ is especially preferred. Afoam density of about 1100 kg/m³ is especially preferred. Obviously, anydensity comprised between the aforementioned densities are deemedsuitable with respect to the density of the substrate.

The cells of a foam layer may have an average size (largest dimension)of from about 0.05 mm to about 5.0 mm, especially from about 0.1 toabout 3.0 mm, as measured by ASTM D-3576-98.

1.8 Plasticizer

In a preferred embodiment, the present invention provides a coveringpanel according to the first aspect of the invention, wherein saidsubstrate comprises one or more plasticizers in an amount of less than15 wt. %, based on the total weight of said substrate.

In a preferred embodiment, the present invention provides a coveringpanel according to the first aspect of the invention, wherein saidsubstrate comprises one or more plasticizers in an amount of less than10 wt. %, based on the total weight of said substrate. More preferably,said amount of one or more plasticizers in said substrate is comprisedin an amount of less than 5 wt. %, based on the total weight of saidsubstrate, and even more preferably, in an amount of less than 2 wt. %.

This is advantageous, because a reduced amount of one or moreplasticizers provides a substrate with high elasticity modulus. Saidhigh elasticity modulus corresponds to a high rigidity of the obtainedpanel and results in a reduced amount of curling of the finishedcovering panel.

The term “plasticizer” as referred herein is to be understood as acompound used to increase the fluidity or plasticity of a material,typically a polymer. The plasticizer can be any plasticizer known in theart. For example, the plasticizer may be a phthalic diester, such asdiisononyl phthalate (DINP). Other examples of plasticizer include, butare not limited to ditridecylphthalate, diisodecyl phthalate,dipropylheptyl phthalate, diisooctyl terephthalate (DOTP), benzoates,adipates, any o-phthalate free plasticizers, natural-material basedplasticizers, and the like.

In a preferred embodiment, the present invention provides a coveringpanel according to the first aspect of the invention, whereby saidsubstrate is substantially free of one or more plasticizers.

By the term “substantially free of one or more plasticizers” is to beunderstood that no plasticizers are deliberately mixed with thesynthetic material in order to form a substrate. Accordingly, saidplasticizer is comprised in said substrate in an amount of less than 2wt. %, based on the total weight of said substrate, more preferably inan amount of less than 0.5 wt. %, and even more preferably in an amountof less than 0.1 wt. %. Most preferably, no plasticizer is comprised insaid substrate.

In a preferred embodiment, the present invention provides a coveringpanel according to the first aspect of the invention, whereby any ofsaid top layer is substantially free of one or more plasticizers.

1.9 Polybenzoxazine

In one example, said synthetic material further comprisesbenzoxazine-based polymers. Polybenzoxazine is a class ofhigh-performance materials possesses many intriguing characteristics.The ability of alloying with other minor components is one of thecrucial properties for this novel kind of thermosetting, i.e., theproperties of the rendered alloys and blends could be tailor-made tomeet the requirements of any application because they possess good flameretardance, and thermal properties of phenolic resins, including theirhigh mechanical properties, with good sound and noise absorbance. Inaddition, polybenzoxazines render near-zero volumetric shrinkage orexpansion upon cure, high processability due to low melt viscositybefore polymerization, low water uptake, high char yield, and lowcoefficient of thermal expansion. Moreover, the polymers render lowdielectric constant and dissipation loss, high mechanical performanceand great molecular design flexibility. Interestingly, the polymerspossess a crucial property, i.e., the ability to be alloyed with manychemicals such as epoxy, polyurethane. This interesting property leadsto the modification of mechanical and thermal properties of the renderedalloys. That means the drawback of the polybenzoxazine, i.e., itsbrittleness, could be managed by alloying with other polymers.Thermoplastic and/or thermosetting blends or copolymers one or morecomprising benzoxazine-based polymers can be selected from the groupcomprising, but not limited to: benzoxazine/epoxy copolymers,benzoxazine/epoxy/phenolic resins, poly(benzoxazine-urethane) alloys,polybenzoxazine/poly-(N-vinyl-2-pyrrolidone) alloy,polybenzoxazine/poly(ε-caprolactone) blends,poly-benzoxazine/poly(imide-siloxane) alloys, polybenzoxazine/polyimideblends, poly-benzoxazine/dianhydride copolymer, polybenzoxazine/ligninalloys. Other preferably benzoxazine-based synthetic materials aredisclosed in ‘Handbook of Benzoxazine’, Ed. Hatsuo Ishida, Tarek Agag,Elsevier; and in ‘Alloys and Composites of Polybenzoxazines’, S.Rimdusit et al., Engineering Materials, DOI:10.1007/978-981-4451-76-5_2, Springer Science+Business Media Singapore2013.

In one preferred embodiment, said thermoplastic material comprises PVC,PVAc, PE, PS, PP, ABS, PET, PA, blends, and/or copolymers thereof. Inone preferred embodiment, said thermosetting material is PU or a nettingacrylate, or a phenol formaldehyde, or copolymers thereof, or mixturesthereof.

1.10 Reinforcement Layer

In one embodiment, the present invention provides a covering panelaccording to the first aspect of the invention, whereby said substratefurther comprises a reinforcement layer.

1.10.1 Glass Fibre

In one embodiment, a covering panel is comprised of a substratecomprising an upper and a lower substrate. Between the upper substrateand the lower substrate there may be provided a reinforcement layerwhich is a glass fibre fabric that is impregnated with a rigid polyvinylchloride (PVC) material. This reinforcement layer can have the functionto further enhance the dimensional stability to the substrate, toprevent an excessive shrinkage or expansion of the covering panel due toa change of temperature. The reinforcement layer has a high thermalstability, i.e. it hardly changes its dimensions in case of a thermalvariation, especially in the horizontal direction parallel to the upperand lower substrate. That is, the overall dimensional stability of thecovering panel is high even when the substrate or other layers of thepanel have the tendency to shrink or to expand due to a rise or fall ofthe temperature to which the panel is exposed. The present inventorshave found that the provision of the reinforcement layer can furtherreduce a thermal shrinkage or expansion of the panel by up to 50%.Another important advantage of providing a reinforcement layer to thesubstrate is to improve the stability of the panel against localpressure by a sharp object, for example, a piece of furniture. This isdue to the fact that the dense fabric of the glass fibre fabric thatforms the reinforcement layer provides a strong resistance to a localpressure by a sharp or pointed heavy object resting on top of the panel.Even if the top layers resting on the reinforcement layer, especially atleast one of the upper substrate and a print layer, are compressedpunctually to some extent, this local compression will not cause adeterioration or even a lasting damage of the overall structure of thepanel because of the resistance of the reinforcement layer.

In one example of the reinforcement layer, a nonwoven glass fibre fabriccan be used with a surface weight of 65 gsm. Preferably, the glassfibres have an average length of at least 3.0 mm, and preferably anaverage length of at least 4.5 mm.

Preferably, said length is at most 20.0 mm, more preferably at most 12.0mm and even more preferably at most 9.0 mm. The glass fibre fabric beimpregnated with a plastic material such as a PVC material. Fillers canalso be contained in the PVC material for impregnating the glass fibrefabric.

Accordingly, the thermal dimensional stability and the mechanicalstability against local pressure are significantly enhanced. In a morepreferred example, the glass fibre may be impregnated with a plasticmaterial such as a PVC material containing no plasticizer. Fillers canalso be contained in the plastic material for impregnating the glassfibre fabric. In one embodiment for the structure of a covering panel,an upper substrate consists of virgin polyvinyl chloride (PVC), whilethe lower substrate consists of recycled PVC material.

In a one embodiment, the invention provides a panel according to thefirst aspect of the invention, wherein said glass fibres are comprisedin a glass fibre fleece and/or in a glass fibre fabric. Preferably, saidglass fibres are comprised in a glass fibre fleece, such as, forexample, a nonwoven. Such nonwoven glass fibres, in fact, appear to havea better embedding in the thermoplastic matrix, as a result of which astronger and more rigid layer is obtained.

In one embodiment, the invention provides a panel according to the firstaspect of the invention, wherein said glass fibre are pre-treated withan adhesion additive, which is intended to improve the adhesion betweensaid glass fibres and said thermoplastic matrix. For example, said glassfibres are pre-impregnated with the aid of thermoplastic material, suchas, for example, extruded granulate.

In one embodiment, the invention provides a panel according to the firstaspect of the invention, wherein at least said substrate and/or at leastsaid top layer additionally comprises individual reinforcement fibres,wherein said individual reinforcement fibres are not laterallyinterconnected in a network, but are dispersed in a synthetic matrix.Preferably, said reinforcement fibres have a length of at least 0.3 mm,and more preferably at least 1.0 mm. Such reinforcement fibres and/orreinforcement layers are intended to further contribute to thedimensional stability and/or rigidity of said panels according to theinvention, which is one of the objectives to be achieved by the presentinvention.

Preferably, said reinforcement fibres are distributed in said one ormore thermoplastic layers, whether or not in the form of a glass fibrecloth and/or a glass fibre fleece.

Preferably, said reinforcement fibres are comprised in saidthermoplastic layers in a quantity of between 1 and 25 wt. %, and morepreferably between 5 and 15 wt. %, relatively with respect to the totalweight of said reinforcement fibres and thermoplastic layers. Stillpreferably, said fibres meet the description according to the DIN 1259standard. In a first embodiment, said reinforcement fibres compriseglass fibres, however, in an alternative embodiment, also steel fibres,carbon fibres, aramid fibres, polyethylene fibres and/or polypropylenefibres may be used. In yet an alternative embodiment, fibres frombiological origin are used, such as natural fibres as described above.Said reinforcement fibres preferably have an average diameter situatedbetween 1 μm and 100 μm, though more preferably between 3 μm and 30 μm.Most preferably, said average diameter is between 5 μm and 25 μm. In afurther preferred embodiment, said reinforcement fibres are pre-treatedwith an additive or coating to enhance the adhesion between saidreinforcement fibres and said thermoplastic layers, for example, but notlimited to silane. In a further preferred embodiment, reinforcementfibres are selected with a thermal expansion coefficient lower than thethermal expansion coefficient of said thermoplastic layers in which saidfibres are contained and/or with an elastic modulus which is preferablygreater than the modulus of said thermoplastic layers, and preferablygreater than 40 GPa, and more preferably greater than 60 GPa. In anadditional preferred embodiment, said invention provides a panel withreinforcement fibres which have a low thermal expansion coefficient,such as a thermal expansion coefficient of less than 30 μm/m.K and morepreferably less than 5 μm/m.K.

In one embodiment, the present invention provides a panel according tothe first aspect of the invention, wherein said glass fibres have alength of 1 mm or more, and preferably a length of 3 mm or more. In apreferred embodiment, the present invention provides a panel accordingto the first aspect of the invention, wherein said glass fibres have adiameter situated between 5 and 25 μm.

In one embodiment, the invention provides a method according to thesecond aspect of the invention, comprising at least the step of forminga first substrate, wherein preferably said substrate is extruded andsubsequently, immediately, thus in the melt state, arranged on a fibrousmaterial, for example, a glass fibre cloth or a glass fibre fleece. Evenmore preferably, said substrate in the melt state is at least partiallypressed through said fibre material. Thus, a reinforcement layerattached to a substrate is achieved. Preferably, said the thus formedsubstrate comprises a quantity of between 0.25 and 25 wt. % of fibrematerial, and more preferably between 0.5 and 15 wt. %, relative to thetotal weight of said substrate with reinforcement fibres.

In one embodiment, a panel according to the first aspect of theinvention is provided with a glass fibre fabric in the top layer,whereby the top layer is provided on the top surface of a substrate. Inaddition a second substrate layer is provided on the bottom surface ofsaid substrate, whereby said second substrate comprises a glass fibrefabric in a synthetic material.

1.10.2 Alternative Reinforcement Layers

1.10.2.1 Synthetic Fibres

In an alternative embodiment, steel fibres, carbon fibres, aramidfibres, polyethylene fibres and/or polypropylene fibres are used forproviding reinforcement fibres.

In an embodiment of the present invention, the reinforcement material isa nonwoven spun-bond material. A spun-bond nonwoven material ispreferred above other nonwoven materials, such as, for example,needle-punched nonwoven material, since a spun-bond nonwoven materialpossesses high material strength. Preferably, the nonwoven material iscomprised of two synthetic materials, whereby the two syntheticmaterials have a different melting point. The different polymers, wherethe nonwoven material is made from, exist either in separate filamentsor together in one filament. It would therefore be possible that thenonwoven material comprises two filament types. The two filament typesare predominantly made from different polymers with different meltingpoints, so-called bifil types. The term “predominantly” as used hereinmeans at least 90%. It is preferred that the melting points of the twodifferent polymers differ by at least 10° C. More preferably the meltingpoints differ by at least 50° C. Such a product could also be thermallybonded by subjecting the nonwoven product to a temperature in the rangeof the melting point of the polymer with the lower melting point.However, this nonwoven product would not be bonded at each crossingpoint since fibres comprising the polymer with the higher melting pointmight cross each other. Only crossing points of fibres in a combinationhigh and low melting point or low and low melting point would be bondedand not the crossing points of fibres with high melting point. Anonwoven carrier made from bicomponent filaments is therefore preferred.The bicomponent filaments of the nonwoven carrier are thermally bonded.Bicomponent filaments are filaments of two polymers of differentchemical construction. A basic distinction is being drawn between threetypes: side by side types, sheath core types and matrix/fibril types.

The nonwoven material comprises preferably a sheath-core typebicomponent nonwoven material. Preferably, the nonwoven materialcomprises sheath core type bicomponent filaments. Such a sheath-coretype bicomponent nonwoven material possesses a core which acts as abackbone with the sheath being the bonding medium of the backbone. Thestructure of such a product becomes very stable because the filamentsare bonded at each crossing point of the filaments thus creating anonwoven with the highest quantity of bonding points. The dimensionalstability of the nonwoven carrier can be made regular over the lengthand width by optimising the filament distribution. This structure givesenough resistance to the high local impregnation pressure needed forobtaining a smooth impregnated surface over the full width. The greatnumber of bonding points provides a stable nonwoven material already atlow area unit weights while leaving enough open space for penetration ofthe thermoplastic material through the nonwoven textile layer, whichensures good mechanical bonding. The sheath-core type bicomponentnonwoven material possesses a uniform stability. The properties of thedescribed sheath-core type bicomponent nonwoven material make possible astable processing at low weight and thickness. Preferably, thesheath-core type bicomponent nonwoven material comprises a coreconsisting mainly of polyester and a sheath consisting mainly ofpolyamide. Alternatively, the sheath consists mainly of polyamide 6 andthe core consists mainly of polyethylene terephthalate. Preferably thesheath/core ratio lies between 95/5 volume percent and 5/95 volumepercent. More preferably the sheath/core ratio lies between 50/50 volumepercent and 5/95 volume percent. The nonwoven material preferably has abasis weight of 50 gsm to 2500 gsm. More preferably, the nonwovenmaterial has a basis weight of 75 gsm to 1000 gsm. Even more preferably,the nonwoven material has a basis weight of 100 gsm to 350 gsm. Mostpreferably, the nonwoven material has a basis weight of 150 to 280 gsm.A basis weight of the nonwoven material between these limits ensuresthat the nonwoven material is open enough for penetration of thethermoplastic material, ensuring good mechanical bonding.

1.10.2.2 Natural Fibres

In yet a preferred alternative embodiment, natural fibres from plantorigin are used, such as, for example, but not limited to, flax fibre,bamboo fibre, wood fibre, rice fibre.

In one embodiment, the substrate can be any type of substrate suitableto provide a covering with a laminated structure comprising at least onesubstrate onto which a top layer can be applied. In one embodiment, thesubstrate comprises a polymer-based material, a foamed polymer-basedmaterial or any combination thereof and preferably natural fibres, asdescribed above.

In one embodiment, the wear layer of a covering panel according to thefirst aspect of the invention comprises one or more fibres, preferablynatural fibres.

1.11 Impact Modifier

In a preferred embodiment, the present invention provides a coveringpanel according to the first aspect of the invention, whereby saidsubstrate further comprises at least one impact modifier, preferably inan amount from 0.1 to 15 wt. % based on the total weight of saidsubstrate.

Impact modifiers are key additives for increasing flexibility and impactstrength to meet physical property requirements of rigid parts. Impactmodifiers are elastomeric or rubbery in nature, with a lower modulusthan the host polymer. The dispersed rubber phase acts to absorb ordissipate the energy of impact in order to stop craze or crackpropagation. In order to stop craze propagation and achieve good impactmodification, the rubbery phase must be very well dispersed and theimpact modifier must be compatible with the host polymer. Good adhesionis necessary to prevent the cracks from propagating around theelastomeric particle. The rubber particle should also have enoughcohesive strength to prevent the crack from propagating easily throughthe rubber particle. To maintain impact at low temperatures, the glasstransition temperature (T_(g)) of the impact modifier should be verylow.

Selected impact modifiers are provided by, but not limited to, Crompton(Blendex), Atofina (Clearstrength), Kaneka (Kane Ace), Atofina(FinaClear), KRATON Polymers (Kraton D), KRATON Polymers (Kraton G),KRATON Polymers (Kraton FG), Atofina (Durastrength), DuPont (Elvaloy andElvaloy HP), Rohm and Haas (Paraloid, Advastab, Advalube), Kaneka,Optatech (PACREL), DuPont-Dow (Tyrin), Crompton (Royalene), DuPont-Dow(Nordel), ExxonMobil (Vistalon), Crompton (Royaltuf), DuPont (Fusabond),Crompton (Royaltuf), DuPont (Elvaloy PTW), DuPont (Surlyn), Dow(AFFINITY Polyolefin Plastomers, VERSIFY), DuPont-Dow Elastomers(Engage), ExxonMobil (Vistamaxx), Atofina (Lotryl), DuPont (Elvaloy AC),Crompton (Interloy), Atofina (Lotader), DuPont (Fusabond, Elvaloy PTW),Baerlocher (Degalan), Arkema (Durastrength), Akcros.

In a preferred embodiment, the present invention provides a coveringpanel according to the first aspect of the invention, whereby saidsubstrate further comprises stabilizers, processing aids, lubricants,colorants and/or adhesion promoters.

1.12 Stabilizer

The substrate also can include at least one heat stabilizer. Astabilizer typically provides heat stability and/or UV light stabilityto a formulation based on a synthetic material. As a non-limitingexample, when PVC is used as polymer, the stabilizer may be acalcium-zinc stabilizer. A calcium-zinc stabilizer containing about 5.5wt. % or more zinc may be used, such as about 6.0 wt. % to about 10.0wt. % zinc. Specific non-limiting examples of zinc-calcium stabilizersare supplied by Baerlocher. Other examples of stabilizers include, butare not limited to, barium-cadmium stabilizers, barium-zinc stabilizers,organotin stabilizers, epoxidized soybean oils, and the like.

Other ingredients can be present in the substrate, such as flameretardants, UV stabilizers, antistatic agents, wear resistant particles,antimicrobial additives, pigments, processing aids, dispersionadditives, lubricants, colorants, modifying resins, cross-linkingagents, antioxidants, foaming agents, tackifiers, and/or otherconventional organic or inorganic additives commonly used in polymers(e.g., vinyl) used in surface coverings.

1.13 Coupling Agent

As an option, one or more coupling agents can be present in any of theformulations, such as a maleic anhydride. Generally, the coupling agentcan be present in an amount sufficient to permit sufficient coupling ofthe homopolymer and/or other components. Amounts can be, for instance,from about 5 wt. % or less (e.g., about 0.1 wt. % to 4 wt. %). Otheramounts can be used.

1.14 Adhesives

Suitable materials for use as adhesion promotors or adhesives or in anadhesive layer may be the same or different between different layers.Any adhesive capable of bonding a specific layer to another layer iswithin the scope of the present invention. An effective type and amountof adhesive can be determined by one of ordinary skill in the artwithout undue experimentation for a given (foam) layer/(foam) layercombination.

Not to be limited to the following adhesives, a suitable adhesive may bea compound such as a chemical adhesive which, for example can be aone-part or multiple part adhesive such as a two-component polyurethaneliquid adhesive, for example a polyurethane or an epoxy; a film such asdouble sided tape or pressure sensitive adhesive (PSA); or another layeror film comprising a material which is compatible with (i.e., bonds to)both a first and a second layer.

Suitable materials for use as adhesives or in adhesive layers includethose adhesive materials known in the art as useful with plasticsurfaces and foams, see U.S. Pat. No. 5,695,870. Examples includepolyolefin copolymers such as ethylene/vinyl acetate, ethylene/acrylicacid, ethylene/n-butyl acrylate, ethylene ionomers,ethylene/methylacrylate, and ethylene or propylene graft anhydrides.Other useful adhesives include urethanes, copolyesters and copolyamides,styrene block copolymers such as styrene/butadiene and styrene/isoprenepolymers, acrylic polymers, and the like. The adhesives may bethermoplastic or curable thermoset polymers, and can include tacky,pressure-sensitive adhesives. The adhesive or adhesive layer ispreferably recyclable within the panel manufacturing process. Theadhesive material must not negatively impact the physical integrity orproperties of the panel to a substantial degree.

In one embodiment, mechanical means may be used to bond two or morelayers of the present invention. For example, fasteners, snap fits,clips, mounting points, joints, channels, Velcro, and the like may beused. In this embodiment, there can additionally be provided an adhesivelayer between the first and second layers, or any layers which arebonded by this means.

In one embodiment, thermal means may be used to bond or weld togethertwo or more layers of the present invention.

In one embodiment, sonic vibration may be used to bond or weld togethertwo or more layers in accordance with the present invention.

In one embodiment, physical means may be used to bond or weld togethertwo or more layers of the present invention. In one embodiment, chemicalmeans may be used to bond or weld together two or more layers of thepresent invention. In this context, chemical means relates to chemicallycuring adhesives which are reactive materials and require chemicalreaction to convert them from their liquid or thermoplastic state tosolid state upon curing.

In one embodiment, one or more of thermal means, mechanical means,physical means, chemical means, and/or adhesive means, may be used incombination to bond two or more layers to each other. To promoteadhesion or bonding between said two or more layers, one or both of thesurfaces to be bonded may optionally be planed, grooved, scored,roughened, sanded, subjected to a surface modification such as, but notlimited to, i.e. a plasma treatment, a corona treatment, etc. to promotechemical and/or mechanical adhesion.

1.15 Various Additives

The substrate(s) formulation comprises synthetic material, fillers, andoptionally pigments and/or variegated pigments compounded with suitablelubricants and processing aids. Other common additives include any oneor combination of more than one of the following: infrared attenuatingagents (for example, carbon black, graphite, metal flake, titaniumdioxide); nucleating agents (for example, magnesium silicate); flameretardants (for example, brominated flame retardants such as brominatedpolymers, hexabromocyclododecane, phosphorous flame retardants such astriphenylphosphate, and flame retardant packages that may includingsynergists such as, for example, dicumyl and polycumyl); internallubricants (for example, calcium stearate and barium stearate, fattyalcohols, low esterification esters, EVA waxes, etc.) for reducing meltviscosity and enhancing transparency; external lubricants (for examplepolyethylene waxes, oxidized polyethylene waxes, paraffins, metal soaps,high esterification esters, amides, fatty acids, etc.) for reducingfriction between the polymer melt and the extrusion mould; acidscavengers (for example, magnesium oxide and tetrasodium pyrophosphate);UV light stabilizers; thermal stabilizers; and colorants such as dyesand/or pigments.

In a preferred embodiment, the present invention provides a coveringpanel according to the first aspect of the invention, whereby any hereindescribed embodiments are combined to further improve the dimensionalstability of said covering panel.

2. Process of Producing Covering Panels

In a second aspect, the present invention provides a process ofproducing covering panels, such as floor panels, wall panels or ceilingpanels, each covering panel comprising at least one substrate andoptionally a top layer, whereby said at least one substrate comprises asynthetic material and a filler material; the method comprising thesteps of:

-   -   mixing said synthetic material and said filler material, thereby        obtaining a mixture;    -   extrusion of said mixture, preferably through a sheet-profile        extrusion head, thereby obtaining a substrate;    -   optionally, laminating said substrate to a top layer;        thereby obtaining a covering panel, whereby said filler material        is mixed with said synthetic material in an amount from 15 to 75        wt. % based on the total weight of said mixture.

The present panels can be formed using a variety of methods. Forinstance, the floor panel can be formed by individually pre-forming thesubstrate(s) and/or any print layer that contains the print design. Thewear layer can be present as an overlay wear layer or can be formedafterwards. The wear layer can include a protective layer, strengtheninglayer, and the like. The substrate(s) can be individually formed bycalendar rolling, extrusion or other techniques once the formulation forthe substrate(s) are prepared. Then, the layers that constitute theentire sheet or a part thereof can be placed on top of each other in astack in their correct order and subjected to hot pressing using ahydraulic press to form a panel body that can be milled to form thetongue and groove edge profiles.

In a preferred embodiment, said synthetic material and said fillermaterial are mixed, whereby said filler material is mixed with saidsynthetic material in an amount from 15 to 75 wt. % based on the totalweight of said mixture. Subsequently, the mixture is extruded,preferably through a sheet-profile extrusion head, thereby obtaining asubstrate. Said substrate is immediately, that is without cooling of theobtained substrate to a temperature below 120° C., affixed to a toplayer using lamination techniques, using the remaining extrusion heat inthe substrate as the necessary thermal energy to provide for goodadhesion between said substrate and said top layer.

In one example, the panel is manufactured as multiple individual pressedlayers, which are consolidated into a unitary panel. In one example, apanel layup including one or more substrate layers, a print layer, andoptionally a wear layer, are stacked in their correct order andsubjected to hot pressing using a hydraulic press to form a panel. Forinstance, the temperature can range, for example, from about 125° C. toabout 135° C. or other temperatures above or below this range. Thepressure can be, for example, from about 4 MPa to about 18 MPa or otherpressures above or below this range. Generally, the time that thepressure can be applied, for example, is from about 30 seconds to about20 minutes, such as from about 1 minute or any time above or below theseranges. The consolidation to form the panel can be a large panel thatcan be punched or cut up into desired final dimensions of the panel (ormultiple panels). Once the hot pressing to form the consolidated panelis achieved, the panel can optionally be provided with a top coat layeror protective layer, like a UV protective layer, optionally containingwear resistant particles, such as aluminium oxide or other wearresistant particles, which can be applied by of a spray coating, rollercoating, or by application with an air knife coater, curtain coater orthe like.

Subsequently, the thus obtained panel can be then annealed to removestress and achieve dimensional stability. The annealing can occur in anoven or other heating device. The annealing can occur at a temperatureabove the glass transition temperature, as determined by ISO 11357-2 andpreferably at a temperature above the Vicat softening temperature, asdetermined by ISO 306-A-50 and most preferably at a temperature of fromabout 125° C. to about 135° C. This annealing can be done on a conveyorbelt, through an infrared oven or conventional air impinged oven, thespeed can be any suitable speed depending upon the length of the ovenand the temperature setting. For instance, the speed of the conveyorbelt can be about 3 meters per minute to about 10 meters per minute,such as about 3.5 meters per minute to about 8 meters per minute.Afterwards, the panel can be aged at ambient conditions, such as about25° C., for various hours, such as about 1 day (about 24 hrs.), about 2days (about 48 hrs.), about 3 days (about 72 hrs.), or more. Afterwards,the panel can be cut or punched out to panel sizes. Then, the sides ofthe resulting panels can be profiled by cutting (e.g., milling) toimpart the desired locking means, such as i.e. click profiles.

A panel according to the first aspect of the invention can also beobtained, for example, by printing a design directly on the top surfaceof the substrate using any number of printing techniques such as gravureprinting, transfer printing, digital printing, flexo printing, and thelike. Or, a printed thermoplastic film (e.g., PVC) or a wood veneer andthe like can be laminated to the substrate.

A protective coating can then be provided on top of the printed design.Any type of protective coating or wear layer can be used, such as apolyurethane type coating with or without wear resistant particles inthe coating. The protective coating can be applied by conventionaltechniques, such as with a curtain coater, direct roll coater, vacuumcoater, differential roll coater, air knife coater, or spray apparatus.

The top surface of the panel can further have a textured or embossedsurface. Said structure can be imprinted onto the surface of thetransparent finishing layer to imitate i.e. a wood structure. Thisimprinting process can be performed by rolling under heat and pressureto deform the surface of the transparent protective coating.

Additionally, a further protective coating can then be placed on top ofthe textured surface. Any type of protective coating can be used, suchas a polyurethane type coating with or without wear resistant particlesin the coating. The protective coating can be applied by conventionaltechniques, such as with a curtain coater, direct roll coater, vacuumcoater, differential roll coater, air knife coater, or spray apparatus.

In a preferred embodiment, the present invention provides a processaccording to the second aspect of the invention, whereby the surface ofthe extruded substrate is not subjected to a surface modification stepprior to further processing. Thereby, the term “surface modification”refers to process of planing, grooving, scoring, roughening, sanding,corona- or plasma-treatment and the like to modify surfacecharacteristics. This is advantageous, because abrasion of the surfacelayer of a foamed open- or closed-cell substrate yields damage to thecell structure and eventually results in loss of mechanical propertiesof the substrate.

In a preferred embodiment, the present invention provides a processaccording to the second aspect of the invention, whereby said substrateis attached to said top layer at a temperature higher than the softeningpoint but lower than the melt temperature of the principal polymercomprised in said substrate.

The softening point is the temperature at which a material softensbeyond some arbitrary softness. It can be determined, for example, bythe Vicat method (ASTM-D1525 or ISO 306). The term “principal polymer”refers to a polymer in said substrate composition, whereby saidprincipal polymer constitutes the major or predominant part of allpolymer material in said substrate composition.

By using a process whereby said substrate is attached to said top layerat a temperature higher than the softening point but lower than the melttemperature of the principal polymer comprised in said substrate, theheat in said substrate contributes to good adhesion properties betweensaid substrate and said top layer.

In a preferred embodiment, the present invention provides a processaccording to the second aspect of the invention, whereby at least thesurface of said substrate is reheated before attaching said substrate tosaid top layer.

By using a reheating step, using i.e. IR heating, the part of saidsubstrate at the upper surface which is to be connected to said toplayer is locally reheated in order to improve adhesion between saidlayer, without the need for reheating the entire substrate. This resultsin an energetic advantage for the lamination process.

In a preferred embodiment, the present invention provides a processaccording to the second aspect of the invention, whereby said substrateand said top layer are subsequently subjected to a double stacklamination process.

By using a double stack lamination process, both the substrate and thetop layer are guided between a top and bottom roll system therebyconnecting and affixing both layers to each other and providing alaminated panel.

EXAMPLES

By means of further guidance, examples are included to better appreciateand further clarify the teaching of the present invention. Said examplesare intended to assist the description of the invention and are nowhereintended as a limitation of the presently disclosed invention.

Examples 1 to 16

A granulate is formed by compounding of a synthetic material (PVC or amixture of PVC and a PVC/PVAc copolymer comprising a 11% PVAc content,in a 60:40 weight ratio). Together with this synthetic material iscompounded a filler mixture comprising a filler, a stabilizer, aprocessing aid, an impact modifier and a lubricant, in ratio's asdepicted in Table 1. No plasticizer is compounded into the granulate inorder to provide a rigid PVC compound.

In Examples 1 to 4, the selected filler is entirely comprised of chalk.In Examples 5 to 8, the selected filler is comprised of chalk and talcin a weight ratio of 76.5:8.5. In Examples 9 to 12, the selected filleris comprised of chalk and talc in a weight ratio of 68.0:17.0. InExamples 13 to 16, the selected filler is comprised of chalk and talc ina weight ratio of 59.5:25.5. In Examples 17 to 22, other fillers aretested.

TABLE 1 Mixtures of a synthetic material, a filler material andadditives for extrusion of a substrate for producing a covering panelaccording to the invention. extrusion mixture (phr*) PVC/ stabi-process- impact Ex. PVC ⁽¹⁾ PVAc ⁽²⁾ chalk ⁽³⁾ lizer ⁽⁴⁾ ing aid ⁽⁵⁾modifier ⁽⁶⁾ talc ⁽⁷⁾ lubricant ⁽⁸⁾ 1 60 40 85.0 4 0.50 4 2 2 60 40 85.04 0.50 8 2 3 100 85.0 4 0.50 4 2 4 100 85.0 4 0.50 8 2 5 60 40 76.5 40.50 4 8.5 2 6 60 40 76.5 4 0.50 8 8.5 2 7 100 76.5 4 0.50 4 8.5 2 8 10076.5 4 0.50 8 8.5 2 9 60 40 68.0 4 0.50 4 17 2 10 60 40 68.0 4 0.50 8 172 11 100 68.0 4 0.50 4 17 2 12 100 68.0 4 0.50 8 17 2 13 60 40 59.5 40.50 4 25.5 2 14 60 40 59.5 4 0.50 8 25.5 2 15 100 59.5 4 0.50 4 25.5 216 100 59.5 4 0.50 8 25.5 2 17 100 4 0.5 75 2 18 100 4 0.5 2 75 ⁽⁹⁾  19100 4 0.5 2 75 ⁽¹⁰⁾ 20 100 4 0.5 2 75 ⁽¹¹⁾ 21 100 4 0.5 2 75 ⁽¹²⁾ 22 1004 0.5 2 75 ⁽¹³⁾ *parts per hundred of synthetic material, comprising PVCand PVC/PVAc copolymer. ⁽¹⁾ S3160, Vinnolit; ⁽²⁾ S3157/11, Vinnolit; ⁽³⁾Craie Moulue, Omya; ⁽⁴⁾ Baeropan MC 90060P, Baerlocher; ⁽⁵⁾ ParaloidK-125 ER, Dow; ⁽⁶⁾ Paraloid KM-376, Dow; ⁽⁷⁾ Luzenac 1445, Imerys; ⁽⁸⁾Baerolub L-PL, Baerlocher; ⁽⁹⁾ Glass fibre: OC968, Owens Corning; ⁽¹⁰⁾Mica: MKT, Imerys; ⁽¹¹⁾ Wollastonite: Nyglos 12, Imerys; ⁽¹²⁾Wollastonite: Aspect 3992, Imerys; ⁽¹³⁾ Chalk: VS10, Omya.

The obtained granulate is subsequently moulded to substrate test samplesfor determination of physical properties as depicted in Table 2. InExamples 1 to 116, the results show that a distinctive decrease of totalshrink properties is observed with the increase of chalk:talc ratio from1:0 to 59.5:25.5. All tests show that the reduction in total shrink ismainly due to the reduction of the relaxation shrink, which is sought tobe minimized by the invention as it largely affects the occurrence ofcurling of the accordingly obtained covering panels. The decreasedshrinking properties occur concurrent with enhanced stiffness asexpressed by the E modulus. The results also show that total shrink islower for samples comprising 100 wt. % of PVC compared to samplescomprising 40 wt. % of a PVC/PVAc copolymer, although the copolymerexhibits comparatively higher stiffness. Furthermore, in Examples 17 to22, the results show that the addition of other types of filler alsoleads to a distinct improvement of shrink properties. Addition of higheramounts of impact modifier show to negatively impact both the totalshrink and E modulus, leading to conclude that lower amounts of impactmodifier are preferred.

TABLE 2 Physical properties of a covering panel according to theinvention. relaxation shrink melt shrink total shrink E modulus Ex. [%]^(a) [%] ^(b) [%]^(c) [MPa] ^(d) 1 −1.76 −0.31 −2.07 3930 2 −1.81 −0.31−2.12 3690 3 −1.22 −0.33 −1.55 3720 4 −1.31 −0.35 −1.65 3520 5 −1.40−0.28 −1.67 4200 6 −1.53 −0.29 −1.82 4000 7 −1.05 −0.31 −1.35 3980 8−1.00 −0.32 −1.31 3970 9 −1.19 −0.25 −1.44 4470 10 −1.33 −0.26 −1.594360 11 −0.75 −0.27 −1.01 4430 12 −0.85 −0.29 −1.13 4480 13 −1.01 −0.23−1.24 4770 14 −1.08 −0.24 −1.32 4630 15 −0.72 −0.26 −0.98 4770 16 −0.73−0.26 −0.99 4520 17 −0.49 −0.20 −0.69 12300 18 −0.16 −0.14 −0.29 1190019 −0.62 −0.29 −0.91 10500 20 −0.39 −0.16 −0.56 15800 21 −0.52 −0.23−0.75 16100 22 −1.63 −0.43 −2.06 4800 ^(a) For determining shrinkproperties, the length of five extruded test samples was determined fivetimes for each composition to determine an average length value.Subsequently, the samples were subjected to 80° C. for 15 hours andsubsequently stored at room temperature (25° C.) for 24 hours. Bydetermining the length of each sample, the relaxation shrink can bedetermined. ^(b) Melt shrink is determined from the difference betweenmould dimensions and the dimensions of the moulded test samples uponcooling to room temperature. ^(c) Total shrink can be determined frommelt shrink and relaxation shrink. ^(d) E modulus is determinedaccording to ISO 527.

Using the compound of example 15, a substrate of 2 mm thickness isextruded using a sheet-type extrusion head. The substrate issubsequently guided over a roll element, where it is attached to acushion vinyl layer comprising a wear layer of 0.5 mm. In order toimprove the lamination process, the surface of the extruded sheet isre-heated using an IR-heater or a hot air blower to a surfacetemperature of about 100° C. before contacting with the cushion vinyllayer.

Finally, a backing layer is attached to the surface of the substratewhich is not connected to the wear layer and pressed together by adouble stack set-up in order to ensure a rectilinear guidance of thecompressed laminate panel. The inventors have found that such arectilinear guidance reduces curling behaviour of the final coveringpanel product, as determined according to EN 434.

For practical use in surface covering applications, the covering panelcan be dimensioned to suit the appropriate dimensions for transport andinstallation of the covering panels according to standard industrialmethods.

The invention claimed is:
 1. Process of producing covering panelsincluding floor panels, wall panels or ceiling panels, each coveringpanel comprising a top layer and at least one substrate, whereby said atleast one substrate comprises a synthetic material and a fillermaterial; the method comprising the steps of: mixing the syntheticmaterial and the filler material, thereby obtaining a mixture; extrudingsaid mixture, thereby obtaining the substrate; optionally, laminatingthe substrate to the top layer; thereby obtaining the covering panel;annealing the covering panel, wherein said filler material is mixed withsaid synthetic material in an amount from 15 to 75 wt. % based on atotal weight of said mixture and whereby said substrate is attached tosaid top layer at a temperature higher than a softening point but lowerthan a melt temperature of a principal polymer comprised in saidsubstrate.
 2. Process according to claim 1, whereby a surface of theextruded substrate is not subjected to a surface modification step priorto further processing.
 3. Process according to claim 1, furthercomprising the step of printing a design directly on the top surface ofthe substrate, by digital printing.
 4. Process according to claim 1,wherein said filler material is comprised of a mixture of chalk and talcin a ratio of 50:1 to 1:50, based on wt. %.
 5. Process according toclaim 1, wherein said substrate is comprised with a void volume from 10vol. % to 70 vol. %, determined according to ISO 4590 (2016).
 6. Processaccording to claim 1, wherein at least one of said top layer or saidsubstrate is substantially free of one or more plasticizers.
 7. Processaccording to claim 1, whereby said substrate and said top layer aresubsequently subjected to a double stack lamination process.
 8. Processof producing covering panels including floor panels, wall panels orceiling panels, each covering panel comprising a top layer and at leastone substrate, whereby said at least one substrate comprises a syntheticmaterial and a filler material; the method comprising the steps of:mixing the synthetic material and the filler material, thereby obtaininga mixture; extruding said mixture, thereby obtaining the substrate;optionally, laminating the substrate to the top layer; thereby obtainingthe covering panel; annealing the covering panel, wherein said fillermaterial is mixed with said synthetic material in an amount from 15 to75 wt. % based on a total weight of said mixture and whereby at least asurface of said substrate is reheated before attaching said substrate tosaid top layer.
 9. Process according to claim 8, whereby said substrateand the top layer are subsequently subjected to a double stacklamination process.
 10. Process according to claim 8, whereby thesurface of the extruded substrate is not subjected to a surfacemodification step prior to further processing.
 11. Process according toclaim 8, further comprising the step of printing a design directly onthe top surface of the substrate, by digital printing.
 12. Processaccording to claim 8, wherein said filler material is comprised of amixture of chalk and talc in a ratio of 50:1 to 1:50, based on wt. %.13. Process according to claim 8, wherein said substrate is comprisedwith a void volume from 10 vol. % to 70 vol. %, determined according toISO 4590 (2016).
 14. Process according to claim 8, wherein at least oneof said top layer or said substrate is substantially free of one or moreplasticizers.
 15. Process of producing covering panels including floorpanels, wall panels or ceiling panels, each covering panel comprising atop layer and at least one substrate, whereby said at least onesubstrate comprises a synthetic material and a filler material; themethod comprising the steps of: mixing the synthetic material and thefiller material, thereby obtaining a mixture; extruding said mixture,thereby obtaining the substrate; optionally, laminating said substrateto the top layer; thereby obtaining the covering panel; annealing thecovering panel, wherein said filler material is mixed with saidsynthetic material in an amount from 15 to 75 wt. % based on a totalweight of said mixture and wherein the substrate is immediately afterextrusion arranged on a fibrous material, and is at least partiallypressed through said fibrous material.
 16. Process according to claim15, whereby said substrate is attached to said top layer at atemperature higher than a softening point but lower than a melttemperature of a principal polymer comprised in said substrate. 17.Process according to claim 15, whereby at least a surface of saidsubstrate is reheated before attaching said substrate to said top layer.18. Process according to claim 15, whereby said substrate and said toplayer are subsequently subjected to a double stack lamination process.19. Process according to claim 15, further comprising the step ofprinting a design directly on a top surface of the substrate, by digitalprinting.
 20. Process according to claim 15, wherein said substrate iscomprised with a void volume from 10 vol. % to 70 vol. %, determinedaccording to ISO 4590 (2016).